The biosynthesis of proparathyroid hormone (ProPTH) and its conversion to parathyroid hormone (PTH) in mammalian parathyroid glands is under investigation. Emphasis is placed on the chemical structure of the prohormone, other peptides which may be related to PTH in a potential precursor role, the enzymes responsible for the conversion of the prohormone to PTH, the packaging and secretion of PTH and the control of these processes by Ca and other ions. In vitro studies are also planned on tumor tissue from patients suffering hypercalcemia related to malignancy to determine if this type of tissue synthesizes and secretes PTH or a PTH-like peptide.